Sleep-deprived participants were unable to resist 'highly palatable, rewarding snacks,' such as cookies, candy and chips, even when they had consumed a meal that supplied 90 per cent of their daily caloric needs two hours before, researchers said.

The effects of sleep loss on appetite were most powerful in the late afternoon and early evening, times when snacking has been linked to weight gain, researchers said.

Researchers from the University of Chicago in the US recruited 14 healthy men and women in their 20s as volunteers. They monitored the subjects' hunger and eating habits in two situations - one four-day period during which they spent 8.5 hours in bed each night (averaging 7.5 hours of sleep), and another four-day period when they spent only 4.5 hours in bed (4.2 hours asleep).

The participants ate identical meals three times a day, at 9 AM, 2 PM and 7 PM. Researchers measured levels of the hormone ghrelin, which boosts appetite, and leptin, which signals fullness, in their blood.

"We found that sleep restriction boosts a signal that may increase the hedonic aspect of food intake, the pleasure and satisfaction gained from eating," said Erin Hanlon from University of Chicago.